export default function initLoginBg() {
  var windowWidth = document.documentElement.clientWidth || document.body.clientWidth;
  var windowHeight = document.documentElement.clientHeight || document.body.clientHeight;
  // var windowWidth = window.clientWidth;
  // var windowHeight = window.clientHeight;
  var canvas = document.getElementById('canvas') as HTMLCanvasElement,
    ctx = canvas.getContext('2d') as CanvasRenderingContext2D,
    w = canvas.width = windowWidth,
    h = canvas.height = windowHeight,

    hue = 217,
    stars: IntStart[] = [],
    count = 0,
    maxStars = 1500;//星星数量

  var canvas2 = document.createElement('canvas'),
    ctx2 = canvas2.getContext('2d') as CanvasRenderingContext2D;
  canvas2.width = 100;
  canvas2.height = 100;
  var half = canvas2.width / 2,
    gradient2 = ctx2.createRadialGradient(half, half, 0, half, half, half);
  gradient2.addColorStop(0.025, '#CCC');
  gradient2.addColorStop(0.1, 'hsl(' + hue + ', 61%, 33%)');
  gradient2.addColorStop(0.25, 'hsl(' + hue + ', 64%, 6%)');
  gradient2.addColorStop(1, 'transparent');

  ctx2.fillStyle = gradient2;
  ctx2.beginPath();
  ctx2.arc(half, half, half, 0, Math.PI * 2);
  ctx2.fill();

  // End cache

  function random(min: number, max = 0) {
    if (arguments.length < 2) {
      max = min;
      min = 0;
    }

    if (min > max) {
      var hold = max;
      max = min;
      min = hold;
    }

    return Math.floor(Math.random() * (max - min + 1)) + min;
  }

  function maxOrbit(x: number, y: number) {
    var max = Math.max(x, y),
      diameter = Math.round(Math.sqrt(max * max + max * max));
    return diameter / 2;
    //星星移动范围，值越大范围越小，
  }
  interface IntStart {
    orbitRadius: number;
    radius: number;
    orbitX: number;
    orbitY: number
    timePassed: number;
    speed: number;
    alpha: number;
    draw: () => void;
  }
  var Star = function (this: IntStart) {

    this.orbitRadius = random(maxOrbit(w, h));
    this.radius = random(60, this.orbitRadius) / 18;
    //星星大小
    this.orbitX = w / 2;
    this.orbitY = h / 2;
    this.timePassed = random(0, maxStars);
    this.speed = random(this.orbitRadius) / 500000;
    //星星移动速度
    this.alpha = random(2, 10) / 10;

    count++;
    stars[count] = this;
  }

  Star.prototype.draw = function () {
    var x = Math.sin(this.timePassed) * this.orbitRadius + this.orbitX,
      y = Math.cos(this.timePassed) * this.orbitRadius + this.orbitY,
      twinkle = random(10);

    if (twinkle === 1 && this.alpha > 0) {
      this.alpha -= 0.05;
    } else if (twinkle === 2 && this.alpha < 1) {
      this.alpha += 0.05;
    }

    ctx.globalAlpha = this.alpha;
    ctx.drawImage(canvas2, x - this.radius / 2, y - this.radius / 2, this.radius, this.radius);
    this.timePassed += this.speed;
  }

  for (var i = 0; i < maxStars; i++) {
    new Star.prototype.constructor();
  }

  function animation() {
    ctx.globalCompositeOperation = 'source-over';
    ctx.globalAlpha = 0.5; //尾巴
    ctx.fillStyle = 'hsla(' + hue + ', 64%, 6%, 2)';
    ctx.fillRect(0, 0, w, h)

    ctx.globalCompositeOperation = 'lighter';
    for (var i = 1, l = stars.length; i < l; i++) {
      stars[i].draw();
    };

    window.requestAnimationFrame(animation);
  }

  animation();
}
